Although both fighters received the first blemish on their pro records, the Colombian champion kept his belt on the undercard of Israel Vazquez's fourth fight with Rafael Marquez.

Two judges scored the fight 114-114, while a third favored Mares 115-113. The punch stats also were remarkably even, leaving both fighters proclaiming victory and expressing interest in a rematch.

"I won this fight," Perez said through a translator. "It was not a draw. I'm willing to fight a rematch, but it's up to my promoters. He's a good fighter, but he never hurt me."

Perez (20-0-1) was in control for most of the middle rounds of his first title defense, moving Mares around the ring. But Mares (20-0-1) gave a slightly flashier performance, getting off to a strong start and closing with an entertaining finish to his first title shot.

Mares rocked Perez in the final seconds of the 12th round, and the crowd cheered its hometown fighter to the bell. Mares was born in Mexico and fought for the Mexican Olympic team, but lives in the hardscrabble Hawaiian Gardens section of Los Angeles.

"I'm really sad," Mares said. "I thought I won the fight, and I'm not the only one that thought that. I fight for the crowd and for the people, and the crowd saw me win, but the judges didn't. ... In the last round, I thought I was going to knock him out, but he didn't go down."

The 31-year-old Perez didn't start fighting professionally until he turned 26, and he won his title last October with a decision over Joseph Agbeko.

Mares and Perez fought each other and became acquaintances in the amateur ranks. Before the fight, Mares vowed to fight Perez "like a friend, but like a friend that stole my girlfriend."